U.S. patent number 5,541,036 [Application Number 08/046,728] was granted by the patent office on 1996-07-30 for negative photoresist compositions comprising a photosensitive compound, an alkoxymethylated melamine and novolak resin.
This patent grant is currently assigned to Hoechst Japan Limited. Invention is credited to Ralph Dammel, Akihiko Igawa, Masato Nishikawa, Georg Pawlowski.
United States Patent |
5,541,036 |
Igawa , et al. |
July 30, 1996 |
Negative photoresist compositions comprising a photosensitive
compound, an alkoxymethylated melamine and novolak resin
Abstract
A negative photoresist composition comprising: (A) a compound
represented by the following formula (I): ##STR1## wherein R.sup.1
and R.sup.2 which are different from each other represent a
hydrogen atom or a group represented by the following formula (II):
##STR2## (B) an alkoxymethylated melamine, and (C) a novolak resin.
The photoresist composition has resolution below submicron, and can
form resist patterns with an ideal rectangular profile.
Inventors: |
Igawa; Akihiko (Kakegawa,
JP), Nishikawa; Masato (Haibara-gun, JP),
Pawlowski; Georg (Wiesbaden, DE), Dammel; Ralph
(Coventry, RI) |
Assignee: |
Hoechst Japan Limited (Tokyo,
JP)
|
Family
ID: |
14531822 |
Appl.
No.: |
08/046,728 |
Filed: |
April 16, 1993 |
Foreign Application Priority Data
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|
|
|
Apr 28, 1992 [JP] |
|
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4-110285 |
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Current U.S.
Class: |
430/270.1;
522/63; 430/325; 522/166 |
Current CPC
Class: |
G03F
7/038 (20130101); G03F 7/0045 (20130101) |
Current International
Class: |
G03F
7/004 (20060101); G03F 7/038 (20060101); G03C
001/73 () |
Field of
Search: |
;430/270,325
;522/166,63 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Polymer Science Dictionary, Mark Alger, pp. 255-256..
|
Primary Examiner: Rodee; Christopher D.
Assistant Examiner: Weiner; Laura
Attorney, Agent or Firm: Foley & Lardner
Claims
What is claimed is:
1. A negative photoresist composition comprising:
(A) a compound represented by the following formula (I): ##STR5##
wherein R.sup.1 and R.sup.2, which are different from each other,
represent a hydrogen atom or a group represented by the following
formula (II): ##STR6## wherein R.sup.3 and R.sup.4, which may the
same or different from one another, each independently represent a
hydrogen atom or an alkyl group, and R.sup.5, R.sup.6 and R.sup.7,
which may be the same or different from one another, individually
represent a hydrogen atom, a halogen atom, a substituted or
unsubstituted alkyl group in which one or more methylene groups
contained in the alkyl chain may be substituted by an oxygen atom
or a sulfur atom, a cycloalkyl group, an alkenyl group, an aryl
group or an aryloxy group, or two alkyl groups represented by
R.sup.5, R.sup.6 or R.sup.7 may form a 5- or 6-membered ring,
(B) an alkoxymethylated melamine in a monomer ratio of at least
60%, and
(C) a novolak resin wherein the composition is sensitive to i-line
or g-line.
2. A negative photoresist composition according to claim 1, wherein
the compound represented by the formula (I) is a compound in which
R.sup.1 or R.sup.2 represents a group having the formula (II)
wherein R.sup.3, R.sup.4, R.sup.5, R.sup.6 and R.sup.7 represent a
hydrogen atom, or R.sup.3, R.sup.4, R.sup.5 and R.sup.6 represent a
hydrogen atom and R.sup.7 represents a chlorine atom at the
2-position.
3. A negative photoresist composition according to claim 1, wherein
the alkoxymethylated melamine is hexamethoxy methyl melamine.
4. A negative photoresist composition according to claim 1, wherein
the novolak resin is a novolak resin obtained by condensation
between m-cresol and an aldehyde.
5. A negative photoresist composition according to claim 1, wherein
the novolak resin is a novolak resin obtained by condensation
between a phenol mixture containing m-cresol and one or more
phenols selected from the group consisting of p-cresol,
2,4-xylenol, 2,5-xylenol and 3,5-xylenol, and an aldehyde.
6. A negative photoresist composition according to claim 5, wherein
the phenol mixture contains from 85% to 35% by weight of m-cresol,
and from 15% to 65% by weight of one or more phenols selected from
the group consisting of p-cresol, 2,4-xylenol, 2,5-xylenol and
3,5-xylenol.
7. A negative photoresist composition according to claim 1, wherein
the novolak resin has a weight-average molecular weight, calculated
in terms of polystyrene, of 2,000 to 100,000.
8. The negative photoresist composition claimed in claim 1, wherein
the compound of formula (I) is present in an amount of 1/30 to 1/3
by weight of melamine, and the total of said compound of formula
(I) and said malamine is in an amount of 1/20 to 1/2 by weight of
said novolak resin.
9. The negative photoresist composition claimed in claim 1, wherein
the monomer ratio of the alkoxymethylated melamine is at least
80%.
10. A negative photoresist composition sensitive to i-line or
g-line, comprising:
(a) a compound represented by the following formula (I): ##STR7##
wherein R.sup.1 and R.sup.2, which are different from each other,
represent a hydrogen atom of a group represented by the following
formula (II): ##STR8## wherein R.sup.3, R.sup.4, R.sup.5, R.sup.6
and R.sup.7 represent a hydrogen atom, or R.sup.3, R.sup.4, R.sup.5
and R.sup.6 represent a hydrogen atom and R.sup.7 represents a
chlorine atom at the 2-position,
(b) an alkoxymethylated melamine wherein the number of carbon atoms
of the alkoxyl group is from 1 to 4, in a monomer ratio of at least
60%, and
(c) a novolak resin obtained by condensation between a phenol
mixture containing from 85% to 35% by weight of m-cresol, and from
15% to 65% by weight of one or more phenols selected from the group
consisting of p-cresol, 2,4-xylenol, 2,5-xylenol and
3,5-xylenol.
11. The negative photoresist composition claimed in claim 10,
wherein the compound of formula (I) is present in an amount of 1/30
to 1/3 by weight of melamine, and the total of said compound of
formula (I) and said malamine is in an amount of 1/20 to 1/2 by
weight of said novolak resin.
12. The negative photoresist composition claimed in claim 10,
wherein the monomer ratio of the alkoxymethylated melamine is at
least 80%.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to photosensitive resin compositions,
and more specifically to negative photoresist compositions which
are used for the production of semiconductors such as an integrated
circuit (IC) and a large-scale integration (LSI), and a liquid
crystal display (LCD).
2. Related Art
As a photoresist for producing semiconductor devices such as ICs
and LSIs, at the beginning, a cyclized rubber photoresist obtained
by dissolving a cyclized rubber and a photosensitive bisazide in an
organic solvent was used. Irradiation with light to the cyclized
rubber photoresist generates nitrene which brings about the
cleavage of double bonds in the cyclized rubber to cause
polymerization, thereby producing a crosslinked network polymer.
With the improvement in the integration of integrated circuits, a
line & space width in a resist pattern which is formed by a
photoresist has been made narrower year after year. (The term "line
& space width" herein is intended to refer to the width of two
lines of those formed in a resist pattern at regular intervals. A
resist which can reproduce patterns with a narrower line &
space width is a resist capable of forming finer patterns.) Under
such circumstances, the above-described cyclized rubber photoresist
cannot meet the present demand for finer resist patterns any more
because the rubber swells in a solution.
A positive resist prepared by the combination use of a novolak
resin which does not swell in a solution at all and a
naphthoquinone diazide has then been used. Furthermore, not only
the materials for photoresists but light to be used for exposure
has been studied in order to obtain finer patterns, and, as a
result, light having a wavelength of 365 nm, called i-line, has
been substituted for light having a wavelength of 436 nm, called
g-line. Those photosensitive naphthoquinone diazides which can
effectively act in light having such a wavelength have also been
studied and selected.
However, even when the use of such a positive resist consisting of
the novolak resin and the naphthoquinone azide and exposure to
i-line are adopted in combination, the line & space width of a
mass-produced pattern is limited to 0.5 .mu.m, that is, a so-called
submicron level is the limit on a mass production scale.
In order to obtain resolution below submicron, a phase-shifting
method in which a layer called a shifter is partially provided on a
photomask and a phase is shifted to obtain improved resolution is
now being studied. A conventional i-line exposure apparatus can be
employed in this method as it is. However, a negative photoresist
is suitable as a photoresist for this method, so that the
development of negative photoresists is highly expected.
LCDs are also produced by using a photoresist in the same manner as
in the production of semiconductors. When a positive photoresist is
used as the photoresist in the production of LCDs, the resist
remains at the periphery of a panel. This is not very favorable
because the resist remaining at the periphery tends to fall off
during the production of the panel, resulting in decrease in the
production yield of the panel. For this reason, a negative
photoresist which does not remain at the periphery of a panel
during the production thereof is desirable for the production of
LCDs. The development of suitable negative photoresists is
therefore expected.
Some negative photoresists applicable to the above-described
phase-shifting method for producing semiconductors or to the
production of LCDs have been proposed. However, these photoresists
have shortcomings in that they require a developing process using
an organic solvent, and that an extremely long exposure time is
required since their photosensitivity is too low. Furthermore, it
is desirable that the profile of the developed photoresist be
rectangular. It is, however, difficult to obtain an ideal
rectangular profile by using the conventional photoresists. In some
cases, whisker-like raised portions are formed in those areas from
which the resist should be removed completely.
SUMMARY OF THE INVENTION
An object of the present invention is to provide negative
photoresists having various properties which are generally expected
to negative photoresists.
Another object of the present invention is to provide negative
photoresists which have resolution below submicron and, at the same
time, can form resist patterns with an ideal rectangular
profile.
A negative photoresist composition according to the present
invention comprises:
(A) a compound represented by the general formula (I): ##STR3##
wherein R.sup.1 and R.sup.2, which are different from each other
represent a hydrogen atom or a group represented by the following
formula (II): ##STR4## wherein
R.sup.3 and R.sup.4, which may be the same or different from, each
independently represent a hydrogen atom or an alkyl group, and
R.sup.5, R.sup.6 and R.sup.7, which may be the same or different
from one another, represent a hydrogen atom, a halogen atom, a
substituted or unsubstituted alkyl group in which one or more
methylene groups contained in the alkyl chain may be substituted by
an oxygen atom or a sulfur atom, a cycloalkyl group, an alkenyl
group, an aryl group or an aryloxy group, or two alkyl groups
represented by R.sup.5, R.sup.6 or R.sup.7 may form a 5- or
6-membered ring,
(B) an alkoxymethylated melamine, and
(C) a novolak resin.
By using the negative photoresist according to the present
invention, patterns with a line & space width of below the
so-called sub-half-micron level, i.e., less than 0.5 .mu.m, can be
formed on a substrate. In a preferred embodiment of the present
invention, patterns with a line & space width of approximately
0.3 .mu.m can be formed. In addition, patterns with an ideal
rectangular profile can be formed on a substrate by using the
negative photoresist according to the present invention.
Furthermore, unexposed areas of the photoresist layer are
completely removed by an alkaline solution, so that whisker-like
raised portions are not formed in those areas from which the resist
should be completely removed. It was unexpected that such excellent
properties of the photoresist composition can be attained by the
combination use of a specific photosensitive compound and a
resin.
DETAILED DESCRIPTION OF THE INVENTION
The negative photoresist composition according to the present
invention comprises a compound represented by the general formula
(I), a novolak resin and melamine.
Compound of Formula (X)
In the general formula (I) representing the compound which is a
constituent of the composition according to the present invention,
one of R.sup.1 and R.sup.3 represents a hydrogen atom, and the
other represents a group having the general formula (II).
In the general formula (II), R.sup.3 and R.sup.4, which may be the
same or different, each independently represent a hydrogen atom or
a straight or branched alkyl group, preferably a hydrogen or a
C.sub.1-4 alkyl group, and more preferably a hydrogen atom.
A halogen atom represented by R.sup.5, R.sup.6 or R.sup.7 is
preferably fluorine, chlorine or bromine, more preferably fluorine
or chlorine.
R.sup.5, R.sup.6 and R.sup.7 may be the same or different from one
another, and represent a straight or branched alkyl group, a
cycloalkyl group, a straight or branched alkenyl group, an aryl
group such as phenyl, tolyl, xylyl or naphthyl, or an aryloxy group
such as phenyloxy, tolyloxy, xylyloxy or naphthyloxy. It is
preferable that the total number of carbon atoms contained in
R.sup.5, R.sup.6 and R.sup.7 be 12 or less at maximum.
One or more hydrogen atoms contained in an alkyl group represented
by R.sup.5, R.sup.6 or R.sup.7 may be substituted. Preferable
substituents include halogen (preferably fluorine, chlorine or
bromine, more preferably chlorine or bromine), an aryl group and an
aryloxy group.
One or more methylene groups contained in the chain of an alkyl
group represented by R.sup.5, R.sup.6 or R.sup.7 may be substituted
by an oxygen atom or a sulfur atom. Namely, among methylene groups
contained in the alkyl group, a methylene group which is directly
bound to a phenyl group becomes an alkoxy group or an alkylthio
group when substituted by an oxygen atom or a sulfur atom, and a
methylene group which is contained in the chain of the alkyl group
becomes an alkoxyalkyl group or an alkylthioalkyl group when
substituted by an oxygen atom or a sulfur atom. Therefore, in the
present invention, the term "alkyl group" represented by R.sup.5,
R.sup.6 or R.sup.7 is intended to include an alkoxy group, an
alkylthio group, an alkoxyalkyl group and an alkylthioalkyl
group.
Furthermore, two alkyl groups represented by R.sup.5, R.sup.6 or
R.sup.7 may form a 5- or 6-membered ring. Specific examples of such
a ring include a dioxymethylene group bound to the 2- and
3-positions, or to the 3- and 4-positions of the benzene ring in
the general formula (II), and an a-naphthyl or .beta.-naphthyl
group formed with the benzene ring to which R.sup.5, R.sup.6 and
R.sup.7 are bound.
In the composition according to the present invention, preferred
examples of substituted or unsubstituted phenyl in the general
formula (II) contained in the compound having the general formula
(I) include phenyl; 2-, 3- or 4-fluorophenyl; 2-, 3- or
4-chlorophenyl; 2-, 3- or 4-bromophenyl; 2-, 3- or 4-methyl-,
ethyl-, propyl-, butyl-, isobutyl-, hexyl-, nonyl- or
dodecylphenyl; 2-, 3- or 4-methoxy-, ethoxy-, isopropoxy-, butoxy-,
pentoxy-, octyloxy- or decyloxyphenyl; 2,4-dichloro- or
dibromophenyl; 3,4-dichloro- or dibromophenyl; 2,6-dichlorophenyl;
3-bromo-4-fluorophenyl; 2,3-, 2,4-, 2,5-, 3,4- or 3,5-dimethoxy-,
diethoxy-, dibutoxy- or dihexoyphenyl; 2-ethoxy-5-methoxyphenyl;
3-chloro-4-methylphenyl; 2,4-dimethylphenyl; 2-, 3- or
4-methoxyethyl-, ethoxyethyl-, butoxyethylphenyl;
2,4,6-trimethylphenyl; 3,4,5-trimethoxy- or triethoxyphenyl; or
2,3- or 3,4-dioxymethylenephenyl.
Examples of the compound represented by the general formula (I)
which is considered to be more preferably used in the composition
according to the present invention include those compounds in which
R.sup.1 or R.sup.2 is a group having the general formula (II)
wherein R.sup.3, R.sup.4, R.sup.5, R.sup.6 and R.sup.7 represent a
hydrogen atom, or R.sup.3, R.sup.4, R.sup.5 and R.sup.6 represent a
hydrogen atom and R.sup.7 represents a chlorine atom at the
2-position.
The compound of the general formula (I) can be prepared, for
example, by the method described in U.S. Pat. No. 4,619,998 or any
one of other methods similar to it.
Alkoxymethylated Melamine
The alkoxymethylated melamine, a constituent of the composition
according to the present invention, has such a structure that
hydrogen atoms of amino groups contained in melamine are entirely
or partially, preferably entirely, substituted by an alkoxymethyl
group, preferably a C.sub.1-10 alkoxymethyl group, more preferably
a C.sub.1-4 alkoxymethyl group. Although no particular limitation
is imposed on the degree of this alkoxymethylation, it is
preferably 30% or more, more preferably 70% or more. It is also
possible that melamine be alkoxymethylated with two or more
alkoxymethyls having carbon atoms in different numbers.
The alkoxymethylated melamine can be usually obtained by a reaction
between melamine and an aldehyde under acidic condition. By this
reaction, lower polymers having a polymerization degree of 2 to 5
are also produced together with monomers. In the composition
according to the present invention, the monomer ratio of the
alkoxymethylated melamine is preferably 60% or more, more
preferably 80% or more.
Preferred examples of the alkoxymethylated melamine include
methoxymethylated melamine, ethoxymethylated melamine,
propoxymethylated melamine and butoxymethylated melamine.
Commercially available alkoxymethylated melamines can also be
utilized, and examples of such melamines are as follows: "Cymel
(Registered Trademark) 300" (manufactured by Mitsui-Cyanamid, Ltd.,
methoxymethylated melamine., monomer ratio: 85%), "Cymel 303"
(manufactured by Mitsui-Cyanamid, Ltd., methoxymethylated melamine,
monomer ratio: 80%), "Nikalac MW-30HM" (manufactured by Sanwa
Chemical Co., Ltd., methoxymethylated melamine, monomer ratio 95%)
and "Nikalac MW-40" (manufactured by Sanwa Chemical Co., Ltd., a
mixture of methoxy- and butoxymethylated melamines).
The above melamines can be used for preparing the composition
according to the present invention either singly or in combination
of two or more.
Novolak Resin
A compound obtained by condensation between m-cresol and an
aldehyde (e.g. formaldehyde) can be used as the novolak resin which
is a constituent of the composition according to the present
invention. According to a preferred embodiment of the present
invention, it is preferable to use a novolak resin obtained by
condensation between a mixture containing m-cresol and one or more
phenols selected from the group consisting of p-cresol,
2,4-xylenol, 2,5-xylenol and 3,5-xylenol, and an aldehyde.
In the case where the mixture of m-cresol and the phenols is used,
it is preferable to utilize a mixture containing from 85% to 35% by
weight, more preferably from 75% to 45% by weight of m-cresol, and
preferably from 15% to 65% by weight, more preferably from 25% to
55% by weight of one or more phenols selected from the group
consisting of p-cresol, 2,4-xylenol, 2,5-xylenol and 3,5-xylenol.
It is more preferable to utilize a mixture containing from 75% to
45% by weight of m-cresol, from 45% to 15% by weight of p-cresol,
from 8% to 2% by weight of 2,4-xylenol and from 18% to 12% by
weight of 2,5-xylenol; or a mixture containing from 75% to 45% by
weight of m-cresol and from 25% to 55% by weight of
3,5-xylenol.
In the composition according to the present invention, when the
phenols are used together with m-cresol in the aforementioned
proportion, the resulting resist can have a hard surface and, as a
result, can give an improved film-remaining ratio. In addition, it
can form a pattern with a sharp profile having no round edges.
The weight-average molecular weight of the above novolak resin,
calculated in terms of polystyrene, is controlled within the range
of 2,000 to 100,000, preferably 2,000 to 50,000, more preferably
3,000 to 20,000. When the molecular weight of the resin is less
than 2,000, it is hard to obtain a sufficient crosslink density. As
a result, the film-remaining ratio is drastically lowered, and, in
the worst case, all of the images of the resist run. On the other
hand, when the molecular weight of the resin is in excess of
100,000, the crosslink density becomes too high. As a result,
crosslinking is readily caused even by heat, so that those portions
which should be dissolved by an alkaline developing solution are
remained, not dissolved.
Condensation between m-cresol or the mixture of m-cresol and the
above-described phenols, and an aldehyde can be carried out by a
conventional method, for instance, by heating desired phenols and
an acid catalyst (e.g. oxalic acid) placed in a reaction vessel,
adding an aldehyde drop-wise into the mixture while stirring, and
further heating the resulting mixture.
Negative Photoresist Composition
It is preferable that the negative photoresist composition
according to the present invention comprises the compound having
the general formula (I), the alkoxymethylated melamine and the
novolak resin in such a proportion as to fulfill the following
relationship.
The amount of the compound having the general formula (I) is such
that the weight ratio of the compound of formula (I) to the
melamine is preferably in the range of 1/30 or more and 1/3 or
less, more preferably 1/20 or more and 1/5 or less. In the case
where the weight ratio of the compound of formula (I) to the
melamine is less than the above range, it may be that a relatively
large quantity of exposure energy is required, and that the minimum
line & space width also becomes large. On the other hand, when
the amount of the compound of formula (I) is in excess of the above
range, the crosslinking reaction speed may become too fast, and the
sensitivity becomes so high that it cannot be well controlled even
by a stepper, which is a most accurate exposure apparatus among
commercially available ones.
It is also preferable that the total amount of the compound of
formula (I) and the melamine be selected so that the weight ratio
of the compound of formula (I) and the melamine to the novolak
resin will be within the range of 1/20 or more and 1/2 or less,
more preferably 1/10 or more and 1/3 or less. In the case where the
total amount of the compound of formula (I) and the melamine to the
novolak resin is less than the above range, the film-remaining
ratio can be less than 90%; on the other hand, when it is in excess
of the above range, the profile of the resist pattern can be
non-rectangular (a reverse tapered shape whose upper portion is
wider and lower portion is narrower).
According to a preferred embodiment of the present invention, it is
recommended to make the amount of the compound of formula (I) large
when the molecular weight of the novolak resin is small, and to
make the amount of the compound of formula (I) small when the
molecular weight of the novolak resin is large. The relationship
between the molecular weight of the novolak resin and the amount of
the compound (I), which is considered to be the most preferred, is
as shown in below Table 1.
TABLE 1 ______________________________________ Weight-Average
Molecular Compound (I) (weight)/ Weight of Novolak Resin Novolak
Resin (weight) ______________________________________ 3,000 1/16
5,000 1/44 10,000 1/84 20,000 1/124
______________________________________
The negative photoresist composition according to the present
invention is prepared by dissolving the above-described components
in an organic solvent. Any organic solvent can be used for this
purpose as long as the aforementioned components can be dissolved
in it and the resulting resist can be successfully used as a
photoresist. Specific examples of the preferred organic solvent
include glycol ethers such as ethylene glycol monomethyl ether,
ethylene glycol monoethyl ether and propylene glycol monomethyl
ether; glycol ether acetates such as ethylene glycol monoethyl
ether acetate and propylene glycol monomethyl ether acetate; esters
such as ethyl acetate, butyl acetate and ethyl lactate; ketones
such as acetone, methyl ethyl ketone, cyclopentanone and
cyclohexanone; and aromatic hydrocarbons such as toluene and
xylene. In addition, acetonitrile, dimethylformamide, dioxane and
the like can also be used. These solvents can be used either singly
or as a mixture of two or more.
In general, the negative photoresist composition according to the
present invention is prepared by adding the above-described
components to the above solvent(s), where the total amount of the
components is approximately 10% to 40% by weight, preferably 15% to
30% by weight of the solution.
A third component can be added to the negative photoresist
composition according to the present invention within such a range
that it does not mar the effects of the composition. Examples of
such a third component include a surface active agent by which
radial striation that appears when a substrate is coated with a
photoresist can be prevented, a dye by which reflection from a
substrate can be decreased, an ultraviolet absorbing agent by which
exposure light can be absorbed moderately, a sensitizer by which
sensitivity is enhanced, an adhesion-increasing agent by which
adhesion to a substrate can be increased, and an anti-foam agent by
which foaming can be suppressed.
A method for forming a fine pattern by using the negative
photoresist composition thus obtained will be explained. Onto the
surface of a substrate on which a fine pattern is intended to be
formed, the photoresist according to the present invention is
coated by means of spin coating or roller coating so that the
resist layer will have a uniform thickness (preferably about 0.5 to
3.0 .mu.m, more preferably about 1.0 to 2.0 .mu.m), and then dried
on a hot plate or in a convection oven with internal air
circulation. Subsequently, the substrate on which the photoresist
layer is formed is covered with a mask having a desired pattern,
followed by irradiation of light having a wave length of 200 to 500
nm, preferably g-line or i-line. The composition of the present
invention is soluble in an alkaline solution if it is not treated.
However, it becomes insoluble in an alkaline solution after it is
exposed to light. Therefore, when unexposed areas of the
photoresist layer are removed by an alkaline solution after the
exposure, a pattern which is reverse to the pattern formed on the
mask can be formed, that is, developed on the substrate. The
substrate thus obtained is then supplied to the further process of
producing an IC or an LSI. By repeating the above procedure, a
final product such as an IC or an LSI can be produced.
A 0.3-3% aqueous solution of an inorganic alkali such as NaOH or
KOH, or a 2-4% aqueous solution of an organic alkali such as
tetramethyl ammonium hydroxide can be favorably used as the
alkaline solution used for alkaline development.
Experimental
The negative photoresist composition according to the present
invention will now be explained more specifically referring to
Examples. However, the following examples should not be construed
as limiting the present invention.
It is noted that the compounds (1), (2) and (3) used in the
following examples as the compounds represented by the general
formula (I) are as follows:
Compound (1): In the general formula (I), R.sup.1 represents a
hydrogen atom, and R.sup.2 represents a group having the general
formula (II) wherein all of R.sup.3, R.sup.4, R.sup.5, R.sup.6 and
R.sup.7 represent a hydrogen atom;
Compound (2): In the general formula (I), R.sup.2 represents a
hydrogen atom, and R.sup.1 represents a group having the general
formula (II) wherein all of R.sup.3, R.sup.4, R.sup.5, R.sup.6 and
R.sup.7 represent a hydrogen atom; and
Compound (3): In the general formula (I), R.sup.1 represents a
hydrogen atom, and R.sup.2 represents a group having the general
formula (II) wherein R.sup.3, R.sup.4, R.sup.5 and R.sup.6
represent a hydrogen atom and R.sup.7 represents a chlorine atom at
the 2-position.
EXAMPLE 1
3,5-Xylenol and m-cresol were charged in the weight ratio of 3:7,
and condensation-polymerized with formaldehyde in a conventional
manner, thereby obtaining a novolak resin having a weight-average
molecular weight (calculated in terms of polystyrene) of 5,000 and
a glass transition temperature of 105.degree. C. The compound (1)
and hexamethoxy methyl melamine ("Cymel (Trademark) 300"
manufactured by Mitsui-Cyanamid, Ltd.) were also prepared.
The above-obtained novolak resin, the compound (1) and the
hexamethylol melamine were dissolved in a solvent, polypropylene
glycol monoethyl ether acetate, whereby a photoresist composition
was obtained. In this process, the components were charged so that
the weight ratio of the compound (1) to the hexamethoxy methyl
melamine would be 1/10, and the weight ratio of the total of the
compound (1) and the hexamethylol melamine to the novolak resin
would be 1/4.
The photoresist composition thus obtained was coated onto a silicon
wafer by means of spin coating, and then dried on a hot plate at a
temperature of 90.degree. C. Thus, a resist layer with a thickness
of 1.0 .mu.m was provided on the silicon wafer.
This silicon wafer was exposed by using an i-line stepper NSR
1755i7A (manufactured by Nikon Corp.) through a mask, and baked on
a hot plate at a temperature of 100.degree. C. The wafer was then
developed by a 2.38% aqueous solution of tetramethyl ammonium
hydroxide. As a result, a pattern which was reverse to the pattern
formed on the mask used was formed on the wafer by the resist. By
the electron-microscopic observation of this resist pattern, it was
found that the pattern was resolved to the line & space width
of 0.3 .mu.m, that the profile of the resist was ideally
rectangular, and that no whisker-like raised portions or the like
were observed. The exposure energy required to resolve the line
width and the space width of the resist to 1:1 was 70 mJ/cm2, and
the film-remaining ratio at this exposure energy was 97%. The
profile of the smallest resist line resolved was observed by an
electron microscope, and the rectangular degree of the profile of
the resist was evaluated by the ratio (b/a) of the length of the
lowermost part (a) of the profile to that of the uppermost part
(b). As a result, this value was 1.0, and the profile of the resist
line was thus found to have an ideal rectangular shape.
EXAMPLES 2 TO 13
The procedure of Example 1 was repeated except that the components
shown in below Table 2 were used in place of the components used in
Example 1, whereby negative photoresist compositions were
obtained.
By using the above negative photoresist composition, a resist
pattern was formed on a silicon wafer in the same manner as in
Example 1. The minimum line & space width of this resist
pattern, the exposure energy which was required to resolve the line
width and the space width of the resist to 1:1, the film-remaining
ratio at this exposure energy, and the profile of the resist (b/a)
are as shown in Table 2.
EXAMPLE 14
m-Cresol and formaldehyde were condensation-polymerized in a
conventional manner, thereby obtaining a novolak resin having a
weight-average molecular weight (calculated in terms of
polystyrene) of 3.000. The procedure of Example 6 was repeated
except that the above-obtained novolak resin was used in place of
the novolak resin used in Example 6, thereby obtaining a negative
photoresist composition.
By using this negative photoresist composition, a resist pattern
was formed on a silicon wafer in the same manner as in Example 6.
The minimum line & space width of this resist pattern, the
exposure energy which was required to resolve the line width and
the space width of the resist to 1:1, the film-remaining ratio at
this exposure energy, and the profile of the resist (b/a) are as
shown in Table 2.
EXAMPLE 15
m-Cresol, p-cresol, 2,4-xylenol and 2,5-xylenol were charged in the
weight ratio of 50:30:5:15, and condensation-polymerized with
formaldehyde in a conventional manner, thereby obtaining a novolak
resin having a weight-average molecular weight (calculated in terms
of polystyrene) of 10,000. The procedure of Example 2 was repeated
except that the novolak resin thus obtained was used in place of
the novolak resin used in Example 2, whereby a negative photoresist
composition was obtained.
By using this negative photoresist composition, a resist pattern
was formed on a silicon wafer in the same manner as in Example 1.
The minimum line & space width of this resist pattern, the
exposure energy which was required to resolve the line width and
the space width of the resist to 1:1, the film-remaining ratio at
this exposure energy, and the profile of the resist (b/a) are as
shown in Table 2.
EXAMPLE 16
The procedure of Example 1 was repeated except that the compound
(2) was used in place of the compound (1), whereby a negative
photoresist composition was obtained.
By using this negative photoresist composition, a resist pattern
was formed on a silicon wafer in the same manner as in Example 1.
The minimum line & space width of this resist pattern, the
exposure energy which was required to resolve the line width and
the space width of the resist to 1:1, the film-remaining ratio at
this exposure energy, and the profile of the resist (b/a) are as
shown in Table 2.
EXAMPLE 17
The procedure of Example 1 was repeated except that the compound
(3) was used in place of the compound (1), whereby a negative
photoresist composition was obtained.
By using this negative photoresist composition, a resist pattern
was formed on a silicon wafer in the same manner as in Example 1.
The minimum line & space width of this resist pattern, the
exposure energy which was required to resolve the line width and
the space width of the resist to 1:1, the film-remaining ratio at
this exposure energy, and the profile of the resist (b/a) are as
shown in Table 2.
TABLE 2 ______________________________________ Expo- Film- Line
& sure Remain- Ex- Space Energy ing Resist am- (A) + (B) Width
(mJ/ Ratio Profile ple (A)/(B) (C) (.mu.m) cm.sup.2) (%) (b/a)
______________________________________ 1 1/10 1/4 0.35 70 97 1.0 2
1/20 1/4 0.35 83 97 1.0 3 1/30 1/4 0.40 95 96 1.0 4 1/40 1/4 0.45
110 96 1.1 5 1/5 1/4 0.30 62 97 1.0 6 1/3 1/4 0.32 54 97 1.0 7 1/2
1/4 0.35 20 97 1.1 8 1/10 1/10 0.30 82 96 1.0 9 1/10 1/20 0.32 105
90 1.0 10 1/10 1/30 0.35 120 85 1.1 11 1/10 1/3 0.32 65 97 1.1 12
1/10 1/2 0.35 62 96 1.2 13 1/10 1/1.5 0.35 56 96 1.3 14 1/3 1/4
0.30 80 95 1.0 15 1/20 1/4 0.30 75 97 1.0 16 1/10 1/4 0.30 63 97
1.0 17 1/10 1/4 0.30 72 97 1.0
______________________________________
In the table, the symbols (A), (B) and (C) refer to the weight of
the compound of formula (I), the weight of the alkoxymethylated
melamine, and the weight of the novolak resin, respectively.
COMPARATIVE EXAMPLE 1
The procedure of Example 1 was repeated except that
2-(p-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine was
used in place of the compound (1), whereby a negative photoresist
composition was obtained.
By using this negative photoresist composition, a resist pattern
was formed on a silicon wafer in the same manner as in Example 1.
The minimum line & space width of the resist pattern was 0.3
.mu.m. However, even when the exposure energy was increased to 300
mJ/cm2, the line width was narrower than the space width, and the
exposure energy which can resolve the line width and the space
width of the resist to 1:1 was not able to be determined. The
film-remaining ratio and the profile of the resist are as shown in
Table 3.
COMPARATIVE EXAMPLE 2
The procedure of Example 1 was repeated except that a compound
prepared by esterifying 2-naphthoquinonediazide-4-sulfonylchloride
and 2,3,4-trihydroxybenzophenone in the molar ratio of 3:1 was used
in place of the compound (1), whereby a negative photoresist
composition was obtained.
By using this negative photoresist composition, it was tried to
form a resist pattern on a silicon wafer in the same manner as in
Example 1. However, even when the exposure energy was increased to
300 mJ/cm2, images ran and a perfect pattern was not able to be
formed on the wafer.
COMPARATIVE EXAMPLE 3
The procedure of Example 1 was repeated except that
poly(p-hydroxystyrene) having a weight-average molecular weight of
6,000 was used in place of the novolak resin used in Example 1,
whereby a negative photoresist composition was obtained.
By using this negative photoresist composition, a resist pattern
was formed on a silicon wafer in the same manner as in Example 1.
The exposure energy required to resolve the line width and the
space width of the resist to 1:1 was 75 mJ/cm2, which was in a
practical range. However, when the profile of the resist was
observed by an electron microscope, whisker-like raised portions
were found on the laterals of the resist. The resist pattern was
thus unsuitable for practical use.
TABLE 3
__________________________________________________________________________
Comparative (A) + (B) Line & Space Exposure Energy
Film-Remaining Resist Profile Example (A)/(B) (C) Width (.mu.m)
(mJ/cm.sup.2) Ratio (%) (b/a)
__________________________________________________________________________
1 1/10 1/4 0.35 *1 30 *2 2 1/10 1/4 -- *3 -- -- 3 1/10 1/4 0.35 75
96 *4
__________________________________________________________________________
*1: Even at 300 mJ/cm.sup.2 or more, the line & space width was
not resolved to 1:1. *2: Equilateral traingle. *3: Even at 300
mJ/cm.sup.2 or more, no image remained. *4: Whiskerline raised
portions were found on the laterals of resist.
* * * * *